Image sensor and method of manufacturing the same

ABSTRACT

Disclosed are an image sensor and a method of manufacturing the same. A metal wiring consisting of a lower metal wiring, an upper metal wiring, and a plug connecting the lower and upper metal wirings, in which the lower and upper metal wiring are made of a transparent conductive film pattern, is formed on a substrate with devices formed thereon, the devices including a photodiode and gate electrodes. Then, a passivation film, a color filter, and a microlens are sequentially formed on the metal wiring. All or a portion of the metal wiring is formed in a transparent conductive film pattern. As such, the metal wiring is formed on the photodiode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device for converting photons intocharge packets, and more particularly to an image sensor with a metalwiring and a method of manufacturing the image sensor.

2. Description of the Prior Art

An image sensor is a device for converting one or two-dimensionaloptical image into an electrical signal. The image sensor is a kind of asolid-state image sensor which is generally divided into a CMOS(Complementary Metal Oxide Semiconductor) image sensor and a CCD (ChargeCoupled Device) image sensor.

The CMOS image sensor converts an optical image into an electricalsignal, and employs a switch mode to detect outputs one by one using MOStransistors which are made as many as the number of pixels by use ofCMOS manufacturing technique. In particular, the CMOS image sensor hasadvantages in that a driving mode is simple, various scanning modes canbe embodied, and a signal processing circuit can be integrated into asingle chip, which can miniaturize a chip. In addition, the CMOS imagesensor is inexpensive and consumes a low power, because of utilizing acompatible CMOS technique.

The CMOS image sensor generally includes a pixel array and a peripheralcircuit. In particular, the pixel array mainly consists of a photodiodefor receiving incident light and a peripheral cell for converting thereceived light into an electrical signal. The photodiode has to secure aregion occupied by the photodiode to receive much light.

In the case of securing the occupied region, there is a problem in thatthe pixel array is largely sized. In addition, since the region occupiedby the pixel array is determined after a peripheral cell region issecured, there is a limitation of reducing a size of the pixel array.Accordingly, a fill factor (i.e., a ratio of the photodiode to the pixelarray) is up to 30% at present.

Such as, a conventional CMOS image sensor has some advantages, but it isdifficult to enlarge an area to be occupied by the photodiode, which maynot obtain an image of high resolution.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made to solve theabove-mentioned problems contained in the prior art, and an object ofthe present invention is to provide an image sensor capable of enlargingan area to be occupied by a photodiode.

Another of the present invention is to provide a method of manufacturingan image sensor of which an area occupied by a photodiode can be easilyenlarged.

In order to accomplish this object, there is provided an image sensorcomprising: a substrate with devices formed thereon, the devicesincluding a photodiode and gate electrodes; a metal wiring of atransparent conductive material formed on the substrate for transferringsignals of the devices to a circuit; a passivation film formed on themetal wiring for protecting the devices; a color filter formed on thepassivation film for embodying an image; and a microlens formed on thecolor filter for collecting light.

According to another aspect of the present invention, there is provideda method of manufacturing an image sensor comprising the steps of:forming devices including a photodiode and gate electrodes on asubstrate; forming a lower metal wiring of a transparent conductive filmpattern on the substrate to transfer signals of the devices to acirsuit; forming a plug formed on the lower metal wiring, the plug beingconnected to the lower metal wiring; forming an upper metal wiring of atransparent conductive film pattern on the plug, the upper metal wiringbeing connected to the plug; forming a passivation film on the uppermetal wiring; and forming a color filter and a microlens on thepassivation film.

With the present invention, all or a portion of the metal wiringconsisting of the lower metal wiring, the plug, and the upper metalwiring is formed in a transparent conductive film pattern. As such, themetal wiring can be formed on the photodiode, so that the area occupiedby the photodiode can be easily enlarged. That is, the metal wiring ofthe transparent conductive film pattern is employed, which does notimpede transfer of light to the photodiode.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view depicting a layout of a pixel array of animage sensor according to a preferred embodiment of the presentinvention;

FIG. 2 is a cross-sectional view of an image sensor according to apreferred embodiment of the present invention; and

FIGS. 3A through 3F are cross-sectional views depicting a process ofmanufacturing an image sensor according to a preferred embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a preferred embodiment of the present invention will bedescribed with reference to the accompanying drawings. In the followingdescription and drawings, the same reference numerals are used todesignate the same or similar components, and so repetition of thedescription on the same or similar components will be omitted.

FIG. 1 is a schematic view depicting a layout of a pixel array of animage sensor according to a preferred embodiment of the presentinvention.

Referring to FIG. 1, a pixel diode includes a photodiode 10 fordetecting light and four transistors, which form a unit pixel. Amongfour transistors, a transfer transistor 12 is to transfer a chargestored in the photodiode to a floating diffusion region, a resettransistor 14 is to reset the floating diffusion region as a supplyvoltage level, a drive transistor 16 serves as a source follower, and aselection transistor 18 is to receive a pixel data enable signal andoutput a pixel data signal.

The pixel array is designed with a metal wiring 20 for transferring asignal to the device. The metal wiring 20 may be designed on thephotodiode 10. The reason is because the metal wiring 20 is made of apattern of a transparent conductive film consisting of a transparentconductive material. More specifically, since the metal wiring 20 doesnot impede when the photodiode 10 receives the light, the metal wiring20 may be formed on the photodiode 10.

Accordingly, it is possible to easily enlarge an area occupied by thephotodiode 10 in the pixel array. In practice, a ratio of the photodiodeto the pixel array can be increased by above 50%.

A process of manufacturing the image sensor made of the transparentconductive film according to the present invention will now bedescribed.

Devices containing photodiodes and gate electrodes are formed on asubstrate. More specifically, a device isolation film is formed on thesubstrate. At that time, a trench isolation film is selected as thedevice isolation film. Then, the photodiodes and the gate electrodes areformed on the substrate. At that time, the gate electrode is formed as atransistor. An interlayer insulation layer is formed on the substrate,and then the substrate is subjected to a contact forming process toachieve an electric connection.

After the devices on the substrate, a process of forming a metal wiringis implemented with respect to the substrate. More specifically, atransparent conductive film of a transparent conductive material isformed on the substrate. The transparent conductive material is selectedfrom InO, SnO, ZnO, MgO, or the like. Any one of the above materials ispreferably selected, but a mixture of at least two elements may beutilized. In the case of the transparent conductive film of thetransparent conductive material, a single film is preferably formed onthe substrate, but at least two films may be formed thereon. Forexample, the transparent conductive film may be composed of a first InOfilm and a second SnO film. The transparent conductive film is patternedto form a transparent conductive film pattern and thereby form a metalwiring. More specifically, after forming the transparent conductivefilm, the substrate is subjected to an oxygen plasma process or athermal annealing process under an oxygen atmosphere, so as to form themetal wiring. Te oxygen plasma process is preferably implemented underconditions of a pressure of 5 to 10⁻⁵ Torr and a power of 100 to 1,000W. The thermal annealing process is preferably implemented at atemperature of about 350 to 600° C.

The metal wiring consists of a lower metal wiring, an upper metalwiring, and a plug for connecting the lower and upper metal wirings.Accordingly, after forming the lower metal wiring of the transparentconductive film pattern the above process, the plug connected to thelower metal wiring is formed, and then the upper metal wiring connectedto the upper metal wiring is formed, thereby completing the metalwiring. At that time, the upper metal wiring may be formed by the sameprocess as that of the lower metal wiring. Preferably, the plug is atungsten plug, and may be made of a transparent conductive material.Preferably, an interlayer insulation film pattern is interposed betweenthe lower metal wiring and the upper metal wiring so as to form theplug.

After forming the metal wiring, a passivation film is formed on themetal wiring so as to protect the underlaid devices from being subjectedto the external environments. Then, a color filter is formed on thepassivation film to embody an image. At that time, the color filtermainly consists of red R, green G, and blue B. A microlens is formed onthe color filter to collect incident light.

As such, the image sensor according to the present invention includes,as shown in FIG. 2, a substrate 100 with devices consisting ofphotodiodes and gate electrodes formed thereon, a metal wiring 120 of atransparent material formed on the substrate 100, a passivation film 160formed on the metal wiring 120, a color filter 180 formed on thepassivation film 160, and a microlens 200 formed on the color filter180. The metal wiring 120 consists of a lower metal wiring 120 a, a plug120 b, and an upper metal wiring 120 c. In particular, because of theplug 120 b, an interlayer insulation film pattern 140 is interposedbetween the lower metal wiring 120 a and the upper metal wiring 120 c.

As such, the image sensor of the present invention includes the metalwiring 120 made of the transparent conductive material. The reason whythe metal wiring 120 is formed on the photodiode is because the metalwiring 120 does not block the light incident onto the photodiode.Accordingly, the area occupied by the photodiode can be enlarged.Increased ratio of the photodiode to the pixel array may allow an imageof a high resolution to obtain.

A process of manufacturing the image sensor according to one preferredembodiment of the present invention will now be described in detail withreference to the accompanying drawings.

FIGS. 3A through 3F are cross-sectional views depicting a process ofmanufacturing an image sensor according to a preferred embodiment of thepresent invention.

Referring to FIG. 3A, devices are formed on a substrate through afront-end-of-line (FEOL) process. First of all, a transistor consistingof a gate electrode 32 and a source/drain electrodes 36 a and 36 b isformed on the substrate. An interlayer insulation film pattern 40 havinga contact hall is formed on the substrate 30 with the transistor formedthereon, and a tungsten plug 34 is formed in the contact hall. As aresult, the substrate 30 including the devices having the photodiode andthe gate electrode 32 of the transistor has been provided.

Referring to FIGS. 3B and 3C, a lower metal wiring 50 a is formed on thesubstrate 30 with the devices formed thereon. More specifically, atransparent conductive film 50 of In₂O₃ is formed on the substrate 30.The transparent conductive film 50 may be formed by layering In₂ on thesubstrate through sputtering and then oxidizing a surface of the In₂layer through an oxygen plasma process. At that time, the oxygen plasmais implemented under conditions of a pressure of about 5 Torr and apower of about 500 W. For the thermal annealing process, it ispreferably implemented at a temperature of about 350 to 600° C. Thetransparent conductive film 50 of In₂O₃ is formed on the substrate 30through lamination and surface oxidization. Then, a photoresist film isformed on the transparent conductive film 50, and then is subjected to aphotolithography etching process to form a photoresist pattern 52. Thesubstrate is etched using the photoresist pattern 52 as an etching maskto form the lower metal wiring 50 a of the transparent conductive filmpattern. At that time, the etching is implemented by wet etching, inwhich it uses an etching solution mixed with HCl and H₂O at a ratio of1:1, and the substrate is immersed into the etching solution at about50° C. during about 1 minute

Referring to FIG. 3D, an interlayer insulation film is formed on thesubstrate 30 with the lower metal wiring 50 a formed thereon. At thattime, an oxide film is generally selected as the interlayer insulationfilm. The interlayer insulation film is patterned to form an interlayerinsulation film pattern 60 having a via hole. A plug 50 b of tungsten isformed in the via hole of the interlayer insulation film pattern 60.Formation of the plug 50 b is achieved by lamination and polishing. Morespecifically, after a tungsten film is formed on the interlayerinsulation film pattern 60 in such a way that the tungsten issufficiently buried in the via hole, the tungsten film is polished untila surface of the interlayer insulation film pattern 60 is exposed,thereby obtaining the plug 50 b.

Referring to FIG. 3E, an upper metal wiring 50 c to be connected to theplug 50 b is formed on the substrate. The upper metal wiring 50 c isformed by the same process as that of the lower metal wiring 50 a. Thatis, a transparent conductive film is formed on the substrate, and thenis patterned to form the upper metal wiring 50 c of a transparentconductive film pattern.

As a result, a metal wiring 500 consisting of the lower metal wiring 50a, the upper metal wiring 50 c, and the plug 50 b connecting the wirings50 a and 50 c is formed on the substrate 30.

A passivation film 62 is formed on the substrate 30 with the metalwiring 500 formed thereon. The passivation film 62 is to protect themetal wiring 500 and the devices formed on the substrate from beingpermeated with moisture or being scratched. At that time, an oxide filmis generally selected as the passivation film 62.

Referring to FIG. 3F, a color filter 64 consisting of red, green, andblue is formed on the passivation film 62. The color filter 64 is formedthrough three times of lamination and three times of etching. Morespecifically, a layer forming red is firstly layered and etched, then alayer forming green is layered and etched, and a layer forming red isfinally layered and etched.

A microlens 66 is formed on the color filter 64. At that time, themicrolens 66 is formed in a semi-spherical shape so as to improve anefficiency of collecting the light.

As such, the image sensor consisting of the metal wiring 500, the colorfilter 64, and the microlens 66 is formed on the substrate. The metalwiring 500 can be formed on the photodiode, so that the area occupied bythe photodiode can be enlarged.

With the above description, according to the present invention, themetal wiring can be formed on the photodiode, so that the area occupiedby the photodiode can be easily enlarged. Therefore, an image sensorhaving a high resolution can be obtained by increasing a ratio of thephotodiode to a pixel array.

Although a preferred embodiment of the present invention has beendescribed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. An image sensor comprising: a substrate with devices formed thereon,the devices including a photodiode and gate electrodes; a metal wiringof a transparent conductive material formed on the substrate fortransferring signals of the devices to a circuit; a passivation filmformed on the metal wiring for protecting the devices; a color filterformed on the passivation film for embodying an image; and a microlensformed on the color filter for collecting light.
 2. The image sensor asclaimed in claim 1, wherein the transparent conductive material is atleast one selected from a group consisting of InO, SnO, ZnO, and MgO. 3.A method of manufacturing an image sensor, comprising the steps of:forming devices including a photodiode and gate electrodes on asubstrate; forming a lower metal wiring of a transparent conductive filmpattern on the substrate to transfer signals of the devices to acircuit; forming a plug formed on the lower metal wiring, the plug beingconnected to the lower metal wiring; forming an upper metal wiring of atransparent conductive film pattern on the plug, the upper metal wiringbeing connected to the plug; forming a passivation film on the uppermetal wiring; and forming a color filter and a microlens on thepassivation film.
 4. The method as claimed in claim 3, wherein thetransparent conductive film patterns of the lower and upper metalwirings are at least one selected from a group consisting of InO, SnO,ZnO, and MgO.
 5. The method as claimed in claim 4, wherein thetransparent conductive film patterns of the lower and upper metalwirings are formed by layering a transparent conductive film of atransparent conductive material and then implementing an oxygen plasmaprocess.
 6. The method as claimed in claim 5, wherein the oxygen plasmaprocess is implemented under conditions of a pressure of 5 to 10⁻⁵ Torrand a power of 100 to 1,000 W.
 7. The method as claimed in claim 4,wherein the transparent conductive film patterns of the lower and uppermetal wirings are formed by layering a transparent conductive film of atransparent conductive material and then implementing thermal annealingunder an atmosphere of oxygen gas.
 8. The method as claimed in claim 7,wherein the thermal annealing process is preferably implemented at atemperature of 350 to 600° C.
 9. The method as claimed in claim 3,wherein the plug is made of tungsten or a transparent conductivematerial.
 10. The method as claimed in claim 9, wherein the transparentconductive material is at least one selected from a group consisting ofInO, SnO, ZnO, and MgO.